This invention relates to a recording medium especially adapted for electrophotographic copiers and printers, and to a method for making the same.
Black and color electrophotographic copiers and printers utilize dry toner to form an image on coated and usually calendered paper. As is known, dry toner as used in a copying machine is electrostatically adhered to paper and then heated and fused to the paper. Fusion is the heating and melting of toner on the paper to cause the toner to become attached to and stay on the paper. To fuse the toner, either one or both sides of the paper sheet may be heated.
To obtain good quality copies from an electrophotographic process, the dry toner electrostatically adhered to the paper must be properly heated and fused on the paper. This requires that adequate heat be applied to the toner and paper to cause complete melting of the toner on the paper so that the toner stays on the paper and a good image is obtained. However, the application of too much heat can damage the paper and degrade the resulting image. On the other hand, if too little heat is applied, the toner may not be properly heated and melted and some of the toner may come off of the paper, degrading the quality of the resulting image.
Another cause of image degradation in the electrophotographic process is bubbling. This problem is associated with running coated paper in a high temperature electrophotographic printer. Although the exact cause of bubbling is not known, it is believed that when coated paper is heated to fuse the toner to the surface, the coating acts as a moisture sealant on the base media. When the base media is heated, it is thought that moisture trapped within the base media is vaporized by the heat but is unable to escape due to the coating on opposite sides of the base media, resulting in localized bubbling in the coating. The ability to properly fuse toner on paper at a lower temperature alleviates the bubbling problem.
Another problem encountered in the electrophotographic process has to do with runability of paper sheet through a copier. Runnability refers to the ability of the paper to feed and deliver through a copying machine without causing jams. The runnability of paper is influenced by the "tooth" of its surface, such that a paper surface with more tooth provides for more friction between it and drive rollers of the copier, resulting in improved runnability of the paper through the copier. Obviously, it is not acceptable for paper to excessively jam within a copier.